This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Protein translocations across mitochondria membranes play critical roles in mitochondria biogenesis. The protein transports from the cell cytosol to the mitochondria matrix are carried out by the translocase of the outer membrane (TOM) complex and the translocase of the inner membrane (TIM) complex. In the TIM23 translocon, Tim50 functions as a receptor to guide the precursor with the N-terminal mitochondrion targeting sequence to the inner membrane protein channel for translocation. Recently we have crystallized yeast Tim50. The crystallographic studies on yeast TIM23 translocon will uncover the basic mechanisms how the translocons facilitate the protein translocations across the mitochondria outer and inner membranes.